Thursday, May 11, 2017

Aim: India is dominated by tropical grassy biomes (TGBs), traditionally considered seres or degraded forest, with low diversity relative to the restricted, ancestral wet zone. It is unclear if Indian grasslands and other open habitats are anthropogenically derived or native, old-growth habitats; without a clear timescale of grassland evolution. One way to understand grassland evolution is to study the diversification in taxa restricted to open habitats. We use a dated phylogeny of Ophisops to address questions related to the origin, diversification and inter-relationships of Indian and Saharo-Arabian Ophisops, and ultimately the origin of Indian grasslands and open habitats.

Location: The Indian subcontinent; the Saharo-Arabian Realm.

Methods: We generated up to 2736 base pairs of aligned sequence data (one mitochondrial, two nuclear genes) for Indian lacertids and reconstructed phylogenetic relationships using maximum likelihood and Bayesian inference. We use a fossil-calibrated timetree, diversification analyses and ancestral area reconstructions to test the hypotheses of origin and relationships with Saharo-Arabian Ophisops.

Results: Ophisops is strongly supported as monophyletic, with a basal split into a large-bodied (LBC) and small-bodied clade (SBC). The Saharo-Arabian species are nested within the Indian species in the LBC. Species diversity in Indian Ophisops is grossly underestimated, with 26–47 candidate species. Ophisops began diversifying in the late Oligocene with significant rate shifts in the late Miocene-Pliocene and Pleistocene within the SBC.

Main conclusions: Our results are consistent with an ancient origin of grassland taxa and TGBs in India. Ophisops is a dramatic example of overlooked cryptic diversity outside forests, with ~30 species where five were known. Ophisops dispersed into India from the Saharo-Arabian Realm in the Oligocene with a back dispersal in the Middle Miocene, a novel biogeographical pattern. Diversification in the SBC of Ophisops increased 8-fold during the global C4 grassland expansion. Indian TGBs are old-growth ecosystems that need urgent conservation attention.